The suspect in a shooting at a leading French newspaper office had lived in Britain for several years before returning to France in July, according to the Associated Press.
Abdelhakim Dekhar remains in custody in a suburban Paris hospital after police detained him on Wednesday night, the Paris prosecutor said.
Prosecutor Francois Molins told reporters that the witness who turned Dekhar in said he had been staying with him and that they had met while working in a restaurant together in London 13 years ago.
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Four people have been stabbed in a series of knife attacks at the Notting Hill Carnival.
Mostly fine for Bank Holiday Monday
The bus was travelling to Baton Rouge on Sunday morning to deliver flood relief aid when the crash happened.